1. Field of the Invention
This invention relates to a radiation image storage panel and more particularly, to a radiation image storage panel comprising a support and phosphor layers provided thereon which comprise a binder and a stimulable phosphor dispersed therein.
2. Description of Prior Arts
For obtaining a radiation image, there has been conventionally employed a radiography utilizing a combination of a radiographic film having an emulsion layer containing a photosensitive silver salt material and a radiographic intensifying screen.
As a method replacing the above-described radiography, a radiation image recording and reproducing method utilizing a stimulable phosphor as described, for instance, in U.S. Pat. No. 4,239,968, has been recently paid much attention. In the radiation image recording and reproducing method, a radiation image storage panel comprising a stimulable phosphor (i.e., stimulable phosphor sheet) is used, and the method involves steps of causing the stimulable phosphor of the panel to absorb radiation energy having passed through an object or having radiated from an object; exciting the stimulable phosphor with an electromagnetic wave such as visible light and infrared rays (hereinafter referred to as "stimulating rays") to sequentially release the radiation energy stored in the stimulable phosphor as light emission (stimulated emission); photoelectrically converting the emitted light to give electric signals; and reproducing the electric signals as a visible image on a recording material such as a photosensitive film or on a displaying device such as CRT.
In the above-described radiation image recording and reproducing method, a radiation image can be obtained with a sufficient amount of information by applying a radiation to the object at considerably smaller dose, as compared with the case of using the conventional radiography. Accordingly, this radiation image recording and reproducing method is of great value especially when the method is used for medical diagnosis.
The radiation image storage panel employed in the above-described radiation image recording and reproducing method has a basic structure comprising a support and a phosphor layer provided on one surface of the support. Further, a transparent film is generally provided on the free surface (surface not facing the support) of the phosphor layer to keep the phosphor layer from chemical deterioration or physical shock.
The phosphor layer comprises a binder and stimulable phosphor particles dispersed therein. The stimulable phosphor emits light (stimulated emission) when excited with stimulating rays after having been exposed to a radiation such as X-rays. Accordingly, the radiation having passed through an object or having radiated from an object is absorbed by the phosphor layer of the radiation image storage panel in proportion to the applied radiation dose, and a radiation image of the object is produced in the radiation image storage panel in the form of a radiation energy-stored image (latent image). The radiation energy-stored image can be released as stimulated emission (light emission) by applying stimulating rays to the panel, for instance, by scanning the panel with stimulating rays. The stimulated emission is then photoelectrically converted to electric signals, so as to produce a visible image from the radiation energy-stored image.
It is desired for the radiation image storage panel employed in the radiation image recording and reproducing method to have a high sensitivity and to provide an image of high quality (high sharpness, high graininess, etc.).
As one of factors to determine the sensitivity of a radiation image storage panel and the quality of the image provided thereby, there is mentioned particle size of a stimulable phosphor employed in the panel. More in detail, the employment of a stimulable phosphor having a larger particle size in the radiation image storage panel generally brings about enhancement in the sensitivity of the panel as well as deterioration of the quality of the image provided by the panel. On the contrary, the employment of a stimulable phosphor having a smaller particle size in the panel brings about enhancement in the quality of the image as well as deterioration of the sensitivity.